#include<vector>
using namespace std;
class Solution {
public:
    int numberOfArithmeticSlices(vector<int>& nums) {
        int n = nums.size();
        if (n < 3)return 0;
        vector<int> dp(n);
        dp[0] = 0, dp[1] = 0;
        for (int i = 2; i < n; i++) {
            dp[i] = nums[i] - nums[i - 1] == nums[i - 1] - nums[i - 2] ? dp[i - 1] + 1 : 0;
        }
        int sum = 0;
        for (auto e : dp) {
            sum += e;
        }
        return sum;
    }
};